This project will show the importance of family based spillover effects from health interventions in calculating cost effectiveness analysis as well as provide novel estimates of causal spousal effects in health behaviors. This is important because, currently, no comparative effectiveness or cost effectiveness analyses account for social spillover benefits of treatments, interventions, or programs designed to increase individual and population level health outcomes. This limits our ability to suggest best practices that weigh the comprehensive benefits, costs, and effectiveness of these programs. These issues will become even more important with the passage of the Affordable Care Act (ACA) as well as the introduction of the Patient- Centered Outcomes Research Institute (PCORI) because of the focus on comparative effectiveness estimates in determining treatment and reimbursement patterns in the US. This project extends prior research by using two complementary clinical datasets and experimental empirical methods to examine the importance of spousal spillover effects in determining health behavior outcomes and examine the theoretical and practical implications these spillover effects have on traditional cost benefit, cost effectiveness, and comparative effectiveness measures of treatments, programs, and interventions. We have two specific aims: Specific Aim #1: Use multiple clinical datasets to estimate causal effects of treatments for health behaviors on the outcomes of spouses. While there is a large literature showing very large and important correlations in health behavior decisions between spouses, there are nearly no causal estimates of these effects. This aim is novel in the literature due to our focus on leveraging experimental data to separate causal and non-causal impacts of spousal health behaviors on individual outcomes. Specific Aim #2: Utilize estimates from Aim 1 to extend cost-effectiveness analysis methods for broader use. Aim 2 will examine the implications of the estimates in Aim 1 and similar estimates of social spillovers from the literature for extending comparative effectiveness methods and evidence to consider these spillovers. In addition to this empirical and theoretical extension, we will create a document to collect plug in values from the literature on social/peer spillovers of substance use and other health outcomes for use by CEA and comparative effectiveness researchers in these areas.